Chemical mechanical polishing method and apparatus for controlling material removal profile

ABSTRACT

A material removal apparatus employing a showerhead with non-planar topography is provided. The showerhead surface includes a plurality of fluid zones to apply a fluid pressure to a backside of a polishing pad while a front side of the polishing-pad polishes a substrate. The varying topography of the showerhead surface and the resulting variable gap between a backside of a polishing pad and the non-planar surface of showerhead provide a well-defined fluid distribution and pressure profile for each zone. Such well-defined fluid distribution and pressure profiles, in turn, establish well-defined material removal rates on the substrate as the polishing pad polishes the substrate.

FIELD

The present invention relates to manufacture of semiconductor integratedcircuits and, more particularly to a method for polishing of conductivelayers for planarization and removal.

BACKGROUND

Chemical mechanical polishing (CMP) of materials has important and broadapplication in the semiconductor industry. CMP is a widely usedtechnique for planarizing metals and dielectrics as well as other typesof layers on semiconductor wafers. CMP is often used to flatten/polishthe profiles that build up in multilevel metal interconnect fabricationschemes.

In a typical CMP process, a substrate such as a semiconductor wafer ismounted on a substrate carrier, often called a head. The wafer surfaceto be polished is pressed against a polishing pad surface and the padand the head are moved with respect to each other. This is typicallydone by rotating the wafer, moving the pad or both. The polishing padmay be a conventional polishing pad or a fixed abrasive polishing pad.Conventional or polymeric polishing pads are usually employed along withpolishing slurries including abrasive particles and chemically reactiveagents. The surface of a fixed abrasive polishing pad typically includesabrasive particles embedded in a matrix material. During processing,imbedded abrasive particles perform polishing with the help of apolishing chemistry, which may or may not contain abrasive particles.

FIG. 1 illustrates an exemplary prior-art CMP system 10 that includes apolishing pad 12, which may be moved with respect to the wafer 14 thatis held by a wafer carrier 16. The polishing pad is placed on a platen18 having a flat surface in which an array of built-in pressure zones 20is formed. Pressure zones provide pressurized fluid such as gas to theunder-side of the polishing pad to act as a cushion and prevent the padfrom touching the platen during processing. By applying a varying gaspressure to the backside of the polishing pad from various zones,polishing rate on the corresponding locations of the wafer surface maybe changed while pressing the surface of the wafer against the padsurface. The pressure zones 20 are often formed concentrically to applylocal pressure on different sections on the surface of the wafer. Duringthe CMP process, the wafer carrier 16 can also be rotated while the pad12 is moved. The wafer 14 is pushed against the polishing pad 12 whilerotating to accomplish material removal. Depending on the pressuredistribution profile created on the backside of the pad, polishing rateof the corresponding regions on the wafer surface may be varied toachieve desired polishing on the wafer. For example, by increasing thepressure about the center of the wafer, higher polishing rates may beobtained at the center of the wafer surface. However, in such systems,pressure applied by the pressure zones of the platen onto differentregions of the wafer is not entirely independent from one another.Pressure from neighboring pressure zones may interfere with each other.In fact, theoretically the center of the wafer should always see thehighest pressure in the setup of FIG. 1. Therefore, control forindividual zones may not be very good.

As the brief review above shows, a need exists for a chemical mechanicalpolishing (CMP) system, which can provide accurate, stable andcontrollable polishing rates on various parts of a wafer.

SUMMARY

The present invention employs a flow assembly with a non-planar surfaceprofile to apply fluid flow to a backside of a polishing pad to cause apolishing side of the polishing pad be forced against a workpiecesurface during the chemical mechanical polishing of the workpiece. Thefluid flow is applied to the polishing pad using a plurality of fluidzones placed in the non-planar flow assembly surface. The fluid flowzones may be arranged into any configuration or array in the flowassembly surface such as concentric or linear. Spaces or regionsprovided in between the zones may be used to substantially isolate thezones from the neighboring zones and may establish ventilation regionsor drains for the fluid leaving the individual zones of the flowassembly.

The flow assembly surface may have any profile or topography, such as araised profile or a recessed profile, which vary the gap between theflow assembly surface and the pad or the workpiece surface at selectedlocations. The gap between the backside of the polishing pad and theflow assembly surface of the present invention is defined as a variablegap. The varying profile of the surface of the flow assembly and theresulting variable gap between the backside of the pad and the surfaceof flow assembly provide a well-defined fluid distribution and pressureprofile for each zone. Such well-defined fluid distribution and pressureprofiles establish well defined polishing rates on the workpiece surfaceas the polishing pad polishes the workpiece surface.

In one embodiment of the present invention, material removal rate fromthe workpiece surface can be controlled by actively varying the flowassembly surface profile or topography by moving the fluid flow zoneswith respect to the pad or the workpiece surface, which adjusts thevariable gap. In another embodiment, the material removal rate can becontrolled by using a flow assembly with a fixed surface profile ortopography, which keeps a fixed variable gap which is shaped by thefixed non-planar flow assembly surface and the polishing pad.

Accordingly in one aspect of the present invention, an apparatus forpolishing a surface of a workpiece includes a carrier configured to holdthe workpiece, a showerhead, having a non-planar surface, providing avariable gap between the non-planar surface and the surface of theworkpiece and a polishing pad with a polishing side and a back sidepositioned within the variable gap. The polishing pad is configured topolish the surface of the workpiece with the polishing side when a fluidflow is applied from the non-planar surface to the backside. The fluidflow is applied from a plurality of fluid flow zones formed in thenon-planar surface and the fluid flow zones are configured to move tocause a change in the topography of the non-planar surface. A feed backcircuit induces a change in the topography of the non-planar surface inresponse to a change in a removal profile to yield a pre-determinedremoval profile.

In another aspect of the present invention, a method of controllingmaterial removal rate from a workpiece surface is provided. The methodincludes the steps of holding the workpiece with a carrier, placing thepolishing pad into the variable gap provided between a non-planarsurface of a showerhead and the workpiece surface; emitting fluid fromthe non-planar surface of the showerhead onto backside of the pad toestablish pressure; establishing relative motion between the pad and theworkpiece surface and removing material from the workpiece surface withpolishing side of the pad.

These and other features and advantages of the present invention will bedescribed below with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior art chemical mechanical polishingapparatus;

FIG. 2A is a schematic side view of an embodiment of a chemicalmechanical polishing apparatus of the present invention including ashowerhead with movable fluid flow zones;

FIG. 2B is a schematic plan view of the shower head shown in FIG. 2A;

FIG. 3A is a schematic side view of the chemical mechanical polishingapparatus of the present invention shown in FIG. 2A, wherein the fluidflow zones of the showerhead have been moved into a center highconfiguration to remove more material from center of a wafer;

FIG. 3B is a graph showing variation of material removal across thediameter of the wafer surface when the shower head in FIG. 3A withcenter high configuration is used;

FIG. 4A is a schematic side view of the chemical mechanical polishingapparatus of the present invention shown in FIG. 2A, wherein the fluidflow zones of the showerhead have been moved into a center lowconfiguration to remove more material from edge of a wafer;

FIG. 4B is a graph showing variation of material removal across thediameter of the wafer surface when the shower head in FIG. 4A withcenter low configuration is used;

FIG. 5 is a schematic side view of an embodiment of a chemicalmechanical polishing apparatus of the present invention including ashowerhead with stepped center high surface with fixed fluid flow zones;

FIG. 6 is a schematic side view of an embodiment of a chemicalmechanical polishing apparatus of the present invention including ashowerhead with convex surface with fixed fluid flow zones;

FIG. 7 is a schematic side view of an embodiment of a chemicalmechanical polishing apparatus of the present invention including ashowerhead with stepped center low surface with fixed fluid flow zones;

FIG. 8 is a schematic side view of an embodiment of a chemicalmechanical polishing apparatus of the present invention including ashowerhead with concave surface with fixed fluid flow zones;

FIG. 9 is a schematic plan view of a shower head having elongated fluidflow zones; and

FIG. 10 is a schematic side view of a showerhead with fluid flow zoneshaving variable surface topography.

DETAILED DESCRIPTION

CMP system of the present invention applies fluid flow from a flowassembly separated from a backside of a polishing pad with a variablegap to cause a polishing or processing side of the polishing pad beforced against a workpiece surface during the chemical mechanicalpolishing of the workpiece. The fluid flow may be applied to thepolishing pad using a flow assembly that has a plurality of fluid flowzones placed in a flow assembly surface. The fluid flow zones may bearranged into any configuration or array in the flow assembly surfacesuch as concentric or linear. Spaces or regions provided in between thefluid flow zones may be used to substantially isolate the fluid flowzones from the neighboring zones and may establish ventilation regionsor drains for the fluid leaving the individual zones of the flowassembly.

The flow assembly surface may have any profile or topography, such as araised profile or a recessed profile, which vary the gap between theflow assembly surface and the pad or the workpiece surface at selectedlocations. Accordingly, when the polishing pad is placed over the flowassembly, the gap between one or more zones and the backside of thepolishing pad may be smaller than the gap between the backside of thepolishing pad and the rest of the zones. Therefore, the gap between thebackside of the polishing pad and the flow assembly surface of thepresent invention is defined as a variable gap. The variable gap betweenthe backside of the polishing pad and the fluid flow zone forming thehighest point on the flow assembly surface may be nearly zero or morethan zero. The varying profile of the surface of the flow assembly andthe resulting variable gap between the backside of the pad and thesurface of flow assembly provide a well-defined fluid distribution andpressure profile for each fluid flow zone. Such well-defined fluiddistribution and pressure profiles, in turn, establish well definedpolishing rates on the workpiece surface as the polishing pad polishesthe workpiece surface.

In one embodiment of the present invention, material removal rate fromthe workpiece surface can be controlled by actively varying the flowassembly surface profile or topography by moving the fluid flow zoneswith respect to the pad or the workpiece surface, which adjusts thevariable gap. In another embodiment, the material removal rate can becontrolled by using a flow assembly with a fixed surface profile ortopography, which keeps a fixed variable gap which is shaped by thefixed flow assembly surface and the polishing pad. Therefore, in thisapplication, a gap between the flow assembly surface and the polishingpad is a variable gap which may be an adjustable or fixed variable gap.In either embodiment, in addition to variable gap feature, fluid flowrates at each zone may also be varied, in which case the process windowwithin which removal rates are varied may be further widened.

In other words flow rate control and variable gap control become twoimportant process knobs that can be varied independent from each otherto control the profile of removal rate. After pushing the polishing padtoward the workpiece surface, the fluid from the zones exits theassembly, partially through the drain region if drains are used, thusreducing fluid flow effects on the neighboring zones. In this design,passages or drains between the zones for the used fluid may or may notbe employed because the variable gap itself introduces differencesbetween the pressures over the various zones with different gap values.FIGS. 2A through 4B exemplify two embodiments of flow assemblies orshowerheads. In these embodiments, fluid flow zones z₁, z₂, z₃ and z₄ ofthe showerheads are movable. The gap between the polishing pad and thesurface of the flow assembly is an adjustable variable gap, which may beadjusted by moving the zones with respect to the polishing pad. Itshould be noted that in these examples each zone is connected to adifferent fluid source. However, it is possible to practice thisinvention by connecting two or more or even all the zones to the samefluid source and then varying the adjustable gap to control the removalrate profiles.

FIGS. 2A-4B exemplify a chemical mechanical polishing system 100 havingan embodiment of a flow assembly 102 or a showerhead of the presentinvention. As shown in FIG. 2A, the showerhead 102 comprises a firstfluid flow zone z₁, a second fluid flow zone z₂, a third fluid flow zonez₃ and a fourth fluid flow zone z₄. In this embodiment, the showerhead102 has four exemplary fluid flow zones, although the showerhead 102 mayhave any number of fluid flow zones to perform the present invention. Aswill be described more fully below, each fluid flow zone z₁-z₄ providesa fluid flow, such as airflow, under a polishing belt 104 or a polishingpad, and force the polishing pad 104 against a front surface 106 of awafer 108. Each fluid flow zone is configured to push the polishing padonto definite or corresponding regions of the front surface 106 of thewafer, i.e., each zone has an approximate corresponding location on thefront surface 106. If the air flow is kept constant for each fluid flowzone, the distance or the gap between a fluid flow zone and thepolishing pad affects the force applied onto the front surface of thewafer by that individual fluid flow zone. Therefore, material removalrate from the corresponding locations on the front surface 106 dependson the magnitude of the gap between the polishing pad and the fluid flowzones.

As exemplified with dotted line, zones z₁ and z₂, may each be moved withrespect to the polishing pad 104 using a moving mechanism (not shown) tovary the gap between these zones and the pad or the front surface 106 ofthe wafer. As illustrated in FIGS. 2A-4B, in this embodiment, the gapbetween the polishing pad 104 and each fluid flow zone z₁-z₄ can bevaried to control the material removal rate on a front surface 106 of awafer 108, and to obtain desired material removal profiles on the frontsurface 106. However, as will be described with reference to FIGS. 5-8,a shower head may also be pre-shaped with a desired profile havingelevated or descended zones to achieve desired material removal profileson a front surface of a wafer. Alternately, a design comprisingpre-shaped zones with capability to move may also be employed.

During the material removal process, a wafer carrier 110 retains thewafer 108, preferably at a fixed elevation so that only the distancebetween the back surface of the polishing pad and the fluid flow zonesvary. The polishing pad 104 may be any of a fixed-abrasive polishingpad, or a more standard polymeric polishing pad. The polishing pad 104includes a first surface or a process surface 112 and a second surfaceor a back surface 114. The polishing pad 104 may preferably be tensionedby a tensioning mechanism (not shown). Process surface 112 of thepolishing pad 104 polishes the surface 110 of the wafer during the CMPprocess. Material removal from the front surface 106 may be performedusing a polishing solution or slurry, which may or may not containabrasive particles. The front surface 106 of the wafer 108 may include aconductive layer such as copper or a dielectric layer that the materialremoval process of the present invention is applied. The polishing pad104 may be moved linearly, preferably bi-linearly, using a movingmechanism (not shown). Alternately, the polishing pad may be round andmay be rotated like in standard rotary CMP tools. Exemplary CMP systemsusing bi-linear motion to polish surfaces are exemplified in thefollowing patents. U.S. Pat. No. 6,103,628 entitled Reverse LinearPolisher with Loadable Housing, U.S. Pat. No. 6,464,571 PolishingApparatus and Method with Belt Drive System Adapted to Extend theLifetime of a Refreshing Polishing Belt Provided Therein, and U.S. Pat.No. 6,468,139 Chemical Mechanical Polishing Apparatus and Method withLoadable Housing, which are owned by the assignee of the presentinvention.

During the CMP process of the present invention, an airflow through theshowerhead 102 is applied onto the back surface 114 of the polishing pad104. Application of the airflow to the polishing pad 104 may beperformed using a plurality of fluid openings 116 formed through thefluid flow zones z₁, z₂, z₃ and z₄. The fluid openings 116 may bearranged into any configuration or array with ventilation openings 118among them. The ventilation openings 118 vent out the air used to pushthe pad against the surface of the workpiece, and optionally theventilation openings may be connected to a vacuum system (not shown) formore efficient ventilation. The fluid openings 116 are formed throughthe fluid flow zones z₁, z₂, z₃ and z₄ to create a fluid flowdistribution profile on the showerhead 102. As shown in FIG. 2B, thefluid flow zones z₁-z₄ may be formed concentrically and each zone may beconnected to a fluid flow controller (not shown) to regulate fluid flowfor each zone. In this embodiment, ventilation openings 118 are depictedas circular slits or circular gaps separating each zone. However, theymay also be formed as holes.

In accordance with the principles of the present invention, by varyingthe distance between the individual fluid flow zones z₁-z₄ and thepolishing pad 104, the profile of material removal rate on correspondingareas of the front surface 106 of the wafer is effectively controlledand sharper removal profiles are obtained. FIG. 3A exemplifies a centerhigh configuration of the showerhead, which is formed by mechanicallymoving the zone z₁ and z₂ closer to the back surface 114 of thepolishing pad 104. The center high configuration aims at removing morematerial from the center region of the front surface of the wafercompared to edge. In this configuration, surface s₁ of the first fluidflow zone z₁ is 0.5 to 5 mils, preferably 1 to 2 mils, higher than thesurface s₂ of the second fluid flow zone z₂. Similarly, the surface s₂is 0.5 to 5 mils, preferably 1 to 2 mils, higher than the surfaces s₃and s₄ of the third fluid flow zones z₃ and the fourth fluid flow zonez₄. This vertical distance between the surfaces of the fluid flow zoneswill be called step height herein below.

As mentioned above, airflow towards the back surface 114 of thepolishing pad 104 pushes the pad against the front surface 106 of thewafer 108 that is held and rotated by the wafer carrier 110.Accordingly, in this center high configuration, air from the zonez₁applies more force per unit area to the polishing pad and thecorresponding polished region on the front surface 106 of the wafer 108when the first zone z₁ is elevated and placed at a first elevatedposition at proximity of the back surface 114 of the polishing pad 104.At the first elevated position, the gap between the back of thepolishing pad and top surface of the first fluid flow zone is smallestin comparison to the other fluid flow zones of the shower head 102. Thegap between the backside of the polishing pad and top surface of thefirst fluid flow zone or the highest point on the showerhead 102 may benearly zero or microscopic. At this position, due to the small gap, theair from the first fluid flow zone z₁ is very effective and causes themost material removal from the front surface 106 of the wafer. Since thefirst fluid flow zone z₁is across a center region of the wafer 108,highest material removal rate occurs at the center region of the frontsurface 106.

The second fluid flow zone z₂ is placed in a second elevated position inwhich the second fluid flow zone z₂ applies less force onto thepolishing pad 104 than the force applied by the first fluid flow zone z₁at the first position. In the second elevated position, the gap betweenthe surface of the second fluid flow zone is larger then the gap betweenthe surface of the first fluid flow zone z₁ and the back surface 114 ofthe polishing pad 104. The force applied by the air from the secondfluid flow zone z₂ causes less material removal from the correspondinglocation on the front surface 106, which surrounds the center region ofthe front surface 106, due to the larger gap. Similarly, the third andthe fourth fluid flow zones z₃ and z₄ cause less material removal froman edge region of the front surface 106 due to their relatively distantthird and fourth elevated positions to the back surface 114 of thepolishing pad 104. The step height between the neighboring zones can beadjusted to obtain desired variations of the center high configurationof the showerhead 102 and the resulting material removal profiles.

FIG. 3B illustrates an exemplary material removal profile curve P_(H)for the wafer 108 when the wafer is polished with the center high showerhead configuration shown in FIG. 3A. This material removal profile maybe changed by varying the step heights between the fluid flow zones. Forexample the curve may be made more convex, by increasing the stepheights between the fluid flow zones z₁-z₂, z₂-z₃ and z₃-z₄. Similarly,the profile curve may be made more flat by decreasing the step heightsbetween the same zones. It is also possible to vary amount of fluid flowfrom the selected fluid flow zones to further adjust the materialremoval profile. In fact it is possible to use the center-highconfiguration shown in FIG. 3A and get a flat removal profile byincreasing flows to the outer zones. Therefore, this unique designreduces high sensitivity of removal rates to flow rate and opens up theprocess window for adjusting the removal profiles at will.

An alternative center-low configuration of the shower head 102 can beseen in FIG. 4A, which can be achieved by moving the first and secondfluid flow zones z₁, z₂ away from the back surface 114 of the polishingpad 104 while leaving the third and fourth fluid flow zones z₃, z₄closer to the back surface 114 of the polishing pad. The center lowconfiguration aims at removing more material from the edge region of thefront surface if all flows at all zones are equivalent. In order toachieve center low removal profile, the first fluid flow zone z₁ ismoved into a first declined position, which locates the first fluid flowzone away from the polishing pad. At the first declined position, thegap between the back of the polishing pad and top surface of the firstfluid flow zone is largest in comparison to the other fluid flow zonesof the showerhead 102. At this position, due to the large gap, the airfrom the first fluid flow zone z₁ is not effective and causes a smalleramount of material removal from the center region of the front surface106.

The second fluid flow zone z₂ is placed in a second declined position inwhich the second fluid flow zone z₂ applies more force onto thepolishing pad 104 than the force applied by the first fluid flow zone z₁at the first declined position. In the second declined position, the gapbetween the surface of the second fluid flow zone is smaller then thegap between the surface of the first fluid flow zone z₁ and the backsurface 114 of the polishing pad 104. The force applied by the air fromthe second zone z₂ causes more material removal from the correspondinglocation on the front surface 106, which surrounds the center region ofthe front surface 106, due to the smaller gap. However, the third andthe fourth fluid flow zones z₃ and z₄ cause the highest material removalfrom an edge region of the front surface 106 due to their smaller gapwith the back surface 114 of the polishing pad 104 in the third andfourth elevated positions. The step height between the neighboring zonescan be adjusted to obtain desired variations of the center lowconfiguration of the showerhead 102 and the resulting material removalprofiles. In this configuration, the step height range between the fluidflow zones z₁-z₂, z₂-z₃ and z₃-z₄ can be between the 0.1 to 10 mils,preferably 0.5 to 2 mils.

FIG. 4B illustrates an exemplary material removal profile curve P_(L)for the wafer 108 when the wafer is polished with the center low showerhead configuration shown in FIG. 4A. This profile may be changed byvarying the step heights between the fluid flow zones. For example thecurve P_(L) may be made more concave, by increasing the step heightsbetween the zones z₁-z₂, z₂-z₃ and z₃-z₄. Similarly, the profile curveP_(L) may be made more flat by decreasing the step heights between thesame zones. Profile may also be changed by changing the individual flowsas discussed in association with FIG. 3B.

In the above embodiments, the position of the zones can be configuredusing smart systems that can monitor removal profile during the materialremoval process. Accordingly, by utilizing an electronic feedbackmechanism or control system, gaps may be automatically adjusted to getthe desired removal profile. Such profile may be changed in-situ duringthe process or before processing each wafer.

FIGS. 5 through 8 exemplify various configurations of pre-shaped orfixed surface profile flow assemblies or showerheads. In theseembodiments, fluid flow zones z₁, z₂, z₃ and z₄ of the showerheads areintegrated and are not movable, although they could also be mademovable. The gap between the polishing pad and the surface of the flowassembly is a fixed variable gap, which is shaped by the fixednon-mobile profile or topography of the flow assembly surface and theback surface of the polishing pad. FIG. 5 shows a center high showerhead200 having a center high zone profile, which is formed using apredetermined step height between the neighboring zones. Air holes 202are formed through the fluid flow zones z₁, z₂, z₃ and z₄, andventilation openings 204 are placed between the fluid flow zones. Inthis embodiment, the fluid zones are shaped as radially descendingsteps. A top surface 201 of the showerhead 200 has generally a steppedconvex shape. Therefore, the gap between the top surfaces of the fluidflow zones z₁, z₂, z₃ and z₄ and the back surface 114 of the polishingpad radially expands, being smallest at the first fluid flow zone z₁ butlargest at the fourth fluid flow zone z₄. This characteristic of theshowerhead 200 can be seen in an alternative center high showerhead 300shown in FIG. 6. In this alternative embodiment, rather than the stepstructure shown in FIG. 5, top surfaces of the zones z₁-z₄ are combinedinto a convex surface 301. Air holes 302 are formed through the fluidflow zones z₁, z₂, z₃ and z₄, and ventilation openings 304 are placedbetween the fluid flow zones. Use of the shower heads 200 and 300 givesimilar center high material removal characteristics demonstrated by thecurve P_(H) in FIG. 3B. This profile may be changed by varying the stepheights between the fluid flow zones, the curvature of the surface 301or the flows in individual zones.

FIG. 7 shows a center low fixed showerhead 400 having a center low zoneprofile, which is formed using a predetermined step height between theneighboring zones. Air holes 402 are formed through the fluid flow zonesz₁, z₂, z₃ and z₄, and ventilation openings 404 are placed between thefluid flow zones. In this embodiment, the fluid zones are shaped asradially ascending steps. A top surface 401 of the showerhead 400 hasgenerally a stepped concave shape. Therefore, the gap between the topsurfaces of the fluid flow zones z₁, z₂, z₃ and z₄ and the back surface114 of the polishing pad radially narrows down, being largest at thefirst fluid flow zone z₁ but smallest at the fourth fluid flow zone z₄.This characteristic of the showerhead 400 can be seen in an alternativecenter low showerhead 500 shown in FIG. 8. In this alternativeembodiment, rather than the step structure shown in FIG. 7, top surfacesof the zones z₁-z₄ are combined into a concave surface 501. Air holes502 are formed through the fluid flow zones z₁, z₂, z₃ and z₄, andventilation openings 504 are placed between the fluid flow zones. Use ofthe shower heads 400 and 500 gives similar center low material removalcharacteristics demonstrated by the curve P_(L) in FIG. 4B. This profilemay be changed by varying the step heights between the fluid flow zones,the curvature of the surface 501, or the flows in individual zones.

Although in the above embodiments flow assemblies are defined as roundwith concentric zones, a showerhead 600 may be elongated, for exampleshaped as a rectangle, as shown in FIG. 9. Zones z₁-z₄ may be shaped asrectangular strips or bars having fluid openings 602. As in the aboveembodiments, ventilation openings 604 or slits can be between the zonesz₁-z₄. Zones can be movable or fixed having center high or center lowconfigurations. A cross section of the showerhead 600, taken along theline B, can be any of the shower head cross sections or side views shownin FIGS. 2A, 3A, 4A and 5-8. In this embodiment, the gap between surfaceof the shower head 600 and the polishing pad held above it may be anadjustable variable gap or a fixed variable gap, which are describedabove.

FIG. 10 exemplifies an alternative flow assembly or showerhead 700placed under a polishing pad 702. Zones z₁-z₂ may preferably beseparated by ventilation openings 703, although ventilation openings maynot be used. In showerhead 700, each exemplary fluid zone z₁-z₂ has avariable topography itself such as high surfaces S₁ and low surfaces S₂.In this example, due to the variable topography of the zones, each zonez₁-z has its own variable gap with the backside of the pad 702.

In the above showerhead embodiments, depending on the vertical positionof the fluid flow zones, the gap established between the showerhead andthe back surface of the polishing pad varies. As described above,non-planar top surface of the showerhead varies the gap between the topsurface of the showerhead and polishing pad. For example, among manyothers, the gap can be large at the edges but smaller at the center ofthe showerheads or, alternatively, the gap can be smaller at the edgesbut large at the center at the showerheads. The gap may be nearly zerobetween the highest point on the showerhead and the backside of thepolishing pad. As opposed to the prior art planar top surface platens,non-planar top surface character of the showerheads and resulting gapvariations provide escape passages for the used air. This is notpossible with the prior art systems. Therefore, in the aboveembodiments, the use of ventilation openings is optional and theshowerheads can be manufactured without ventilation openings. Althoughthe present invention is described using a CMP example, the aboveembodiments can be used to perform an electrochemical mechanicalpolishing (ECMP) process. In ECMP, during the material removal with apolishing pad, an electrical potential difference is applied between theconductive surface and a cathode electrode while an electropolishingsolution wets both. The cathode may be the showerhead or a separateelectrode.

Accordingly, the present invention provides substantially enhancedcontrol for each zone. The present invention provides distinct fluidflow rate distribution profiles. Such well-defined and uniform fluiddistribution, in turn, establishes well-defined polishing rates on thesubstrate as the polishing pad polishes the workpiece surface.

Although various preferred embodiments and the best mode have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications of the exemplary embodiment arepossible without materially departing from the novel teachings andadvantages of this invention.

1. An apparatus for polishing a surface of a workpiece comprising: acarrier configured to hold the workpiece; a showerhead, having anon-planar surface, providing a variable gap between the non-planarsurface and the surface of the workpiece; and a polishing pad with apolishing side and a back side positioned within the variable gap andconfigured to polish the surface of the workpiece with the polishingside when a fluid flow is applied from the non-planar surface to theback side.
 2. The apparatus of claim 1, wherein the fluid flow isapplied from a plurality of fluid flow zones formed in the non-planarsurface.
 3. The apparatus of claim 1, wherein the fluid flow zones areconfigured to move to cause a change in the topography of the non-planarsurface.
 4. The apparatus of claim 3, wherein the fluid zones moveduring the polishing of the surface of the workpiece.
 5. The apparatusof claim 1, wherein the non-planar surface has a center high topography.6. The apparatus of claim 1, wherein the non-planar surface has a centerlow topography.
 7. The apparatus of claim 2, wherein at least one of thefluid flow zones is closer to the back side of the polishing pad thanthe rest of the fluid zones.
 8. The apparatus of claim 2, furthercomprising ventilation regions between the fluid flow zones.
 9. Theapparatus of claim 2, wherein the fluid flow zones are concentric. 10.The apparatus of claim 2, wherein the fluid flow zones are elongatedzones.
 11. The apparatus of claim 1, wherein the fluid flow is appliedfrom a plurality of fluid openings formed in the fluid flow zones. 12.The apparatus of claim 4, further comprising a feed back circuit that inresponse to a change in a removal profile induces a change inthe-topography of the non-planar surface to yield a pre-determinedremoval profile.
 13. The apparatus of claim 2, wherein each zoneincludes a variable topography.
 14. The apparatus of claim 1, wherein apolishing solution is delivered onto the polishing sid of the polishingpad during the polishing of the surface of the workpiece.
 15. A methodof controlling material removal rate from a workpiece surface using apolishing solution, a pad and a shower head with a non-planar surfaceproviding a variable gap between the non-planar surface and theworkpiece surface, wherein the pad has a polishing side and a backside,the method comprising the steps of: holding the workpiece; placing thepolishing pad into the variable gap; emitting fluid from the non-planarsurface onto the backside of the pad to establish pressure; establishingrelative motion between the pad and the workpiece surface, and removingmaterial from the workpiece surface with the polishing side of the pad.16. The method of claim 15, further comprising changing topography ofthe non planar surface to vary material removal profile from the surfaceof the workpiece.
 17. The method of claim 15 wherein the step ofemitting fluid comprises emitting fluid from a plurality of fluid flowzones placed in the non-planar surface.
 18. The method of claim 15further comprising the step of sensing a material removal profile duringthe step of removing and adjusting the variable gap to control thematerial removal profile.